Dear users, In wheat there is variation in leaf architecture; eg some varieties have erect and some have drooping leaves. As a result, some have adaxial side facing sun while some have abaxial side facing sun. As we know, generally there are more stomata in abaxial side. Also, abaxial and adaxial guard cells respond deferentially. In our studies, we are measuring PhotosynQ with light sensor head on adaxial side. I am just wondering, has anyone studied and compared the measured parameters both ways? Which side should light sensor head put on in order to obtain consistent and reliable estimates of photosynthetic efficiency? Your sharing of experience and knowledge would be highly appreciated. Ram Ghimire

I’m not aware of a study comparing the adaxial and abaxial side of wheat leaves. But I think it is a very interesting question. I would try to be consistent with the way you measure, and try to have the sensor always pointing in the direction, where the leaf is experiencing the most sun light. You want to perturb the leaf as little as possible. Of cause it would be interesting to see how big the difference really is, comparing both sides. In any case, I would recommend to measure multiple leaves/positions per plant, to best capture the photosynthetic responses.

The current MultispeQ protocols are, in general, designed to replicate the light intensity to the top of the leaf, but there are red lights on both sides of the leaf clamp, so in principle, it it possible to give light simultaneously to the top and bottom. Of course, one would have to decide mow much light to give to top and bottom, e.g. split it, add a certain fraction to bottom?

In the experiment I was describing, I used the actinic LED on the "top" of the device and oriented it in the same direction as the sun would. Then, to observe the gradient of light saturation, I used a probe (pulsed) LED either on the top (LED#3) or bottom (LED#7), but measured the fluorescence using detector #1 (on the top). The point is that the penetration of the probe light is somewhat limited because the top layers of the leaf tend to strongly absorb it. The fluorescence at wavelengths >710 nm passes pretty well through the leaf. So, the probe LED on each side should preferentially report that side's photochemical efficiency. With the unmodified device, the top and bottom LEDs have different colors (590-600 nm versus 655 nm) so it's not perfect, but if you are adventurous and have the tech savvy, you can change the LEDs. (WARNING: PhotosynQ cannot fix it if you screw it up!)